1. Field of the Invention
The present invention relates to improvements in vent apparatus for protecting a confined space having a vent aperture for relief of an overpressure condition. Conventional vent apparatus is especially useful for covering relief openings in enclosures subject to rapid pressure build-ups such as may occur during explosions or uncontrolled combustion events in bag houses, duct work communicating with the bag houses, processing equipment, duct work leading to and from the processing equipment, buildings, pressure vessels, and other types of commercial and industrial installations where explosions or uncontrolled combustion events producing high overpressures may occur.
Vents of the type described have a vent unit including a vent portion that completely opens when a predetermined overpressure condition, such as an explosion or an uncontrolled fire, occurs in the protected area, thereby relieving the excessive overpressure and preventing untoward damage to equipment, vessels, duct work, building structures, and the like that would otherwise be subjected to potentially catastrophic overpressure events.
More particularly, the invention concerns high overpressure vent structure having a pressure relief portion that is in closing relationship to the vent aperture of the protected area, and that includes recloser structure for at least generally closing off the vent aperture in the event of opening of the pressure of the vent unit under a preselected overpressure condition. The recloser structure includes a spring steel vent aperture recloser panel that is normally maintained in a location out of closing relationship to the vent aperture, but may move into a position closing the vent aperture following opening of the pressure relief portion of the vent unit as a function of its inherent resilience of the spring steel.
Advantages of reclosing of the vent aperture by the recloser structure after opening of the primary vent unit include:                elimination or reduction of the ingress of air and thereby oxygen, thus mitigating the effects of a secondary explosion if the protected area remained exposed to the surrounding atmosphere via the vent opening;        prevention of continuation of combustion of process materials that could cause permanent damage to the protected installation;        improvement of suppression of flames/fire, where inert gas, water mist, or the like, is used as an extinguishment agent, by virtue of the fact that the resulting combustion gases/flames cannot escape through venting holes; and        reduction/elimination of contamination of the protected process zone.        
Releasable mechanism is provided in engagement with the panel normally maintaining the panel in the bent condition thereof, out of the location closing the vent aperture. An actuator is connected to the releasable mechanism for effecting release of the panel upon from command from a sensor unit that senses opening of the vent unit from an overpressure condition.
2. Description of the Prior Art
Explosion vents traditionally have been provided with arupturable sheet of metal that has score lines or interrupted slits that define a line of weakness presenting the relief area of the vent. The amount of overpressure required to open the relief area of the vent is determined by, among other things, the type, thickness, and physical properties of the metal selected for fabrication of the explosion vent, the shape and nature of the line of weakness, the location of the line of weakness in the overall area of the vent, and oftentimes the provision of a series of spaced cross-tabs overlying the line of weakness in predetermined relative dispositions.
An exemplary explosion vent of this type is shown and described in U.S. Pat. No. 6,070,365, wherein a rectangular pressure relief panel is mounted in a frame adapted to be secured across a pressure relief opening. The unitary relief panel is formed from a single sheet of steel, stainless steel, Inconel, or other similar metal, and has a three-sided line of weakness defined by a plurality of interrupted slits. The series of spaced rupture tabs positioned over the line of weakness as shown in the '365 patent, must rupture before the relief area of the panel gives away under a predetermined high overpressure resulting from an explosion or a fast-burning fire.
U.S. Pat. No. 5,036,632 is another example of a conventional rectangular metal sheet explosion vent that has a three-sided line of weakness defined by interrupted slits. A layer of synthetic resin material or the like may be provided in covering relationship to the line of weakness slits. Rupturable tabs are also provided in the type of vent shown and described in the '632 patent that must break before the central section of the panel ruptures along the slit line to relieve an overpressure. An elastomeric sealing gasket or gaskets may be provided around the periphery of the rupturable metal sheet.
U.S. Pat. No. 4,498,261, referred to in the disclosure of the '632 patent, is a rectangular vent panel that opens under a relatively low pressure in which the thin sheet structure is described as being medium impact polystyrene, a relatively soft metal such as aluminum alloy, or a fully annealed stainless steel. Interrupted X-pattern slits extend through the vent panel and define individual lines of weakness that terminate at the apex of the X. A thin sealing membrane having the same area as the rupture panel is adhesively bonded to the rupture panel, and may be formed of polyethylene, stainless steel, or aluminum. Similar structure is shown and described in U.S. Pat. No. 4,612,739.
Although prior art pressure relief vents of the type described do satisfactorily open and relieve predetermined overpressure condition in protected spaces, these vents have remained open, thereby allowing the confined space to have continuing access to the surrounding atmosphere. Following out rush of products of combustion from the explosion or fire and relief of the high pressure, oxygen from the atmosphere is immediately available through the vent aperture that can produce a secondary explosion, exacerbation of a fire, or re-ignition of the fire.